Device for detecting variations in the oxygen content of gases containing small amounts of oxygen



Aug. 20, 1968 c. BoKHovEN ETAL 3,398,358

DEVICE FOR DETECTING VARIATIONS IN THE OXYGEN CONTENT OF GASES CONTAINING SMALL AMOUNTS OF OXYGEN Filed Oct. 22, 1964 2 Sheets-Sheel l @n4/Zu mdd @MVM AUS 20, 1953 c. aoKHovEN ETAL 3,398,358

DEVICE FOR DETECTING VAHIATIONS IN THE OXYGEN CONTENT 0F GASES CONTAINING SMALL AMOUNTS OF OXYGEN Filed Oct. 22, 1964 2 Sheets-Sheet 2 ppm o2 400C T v YL Y v f v y r 20o 40o 60o 80o FA FIC-).2

' o:2 199 ppm O2 130 ppm Y t F|G.3

United States Patent O 3,398,358 DEVICE FOR DETECTING VARIATIONS IN THE OXYGEN CONTENT OF GASES CONTAINING SMALL AMOUNTS OF OXYGEN Cornelis Bokhoven, and Wilhelm J. Hanssen, Geleen, Netherlands, assignors to Stamicarbon N.V., Heerlen, Netherlands Filed Oct. 22, 1964, Ser. No. 405,718 Claims priority, application Netherlands, Oct. 22, 1963, 299,586 2 Claims. (Cl. 324-29) ABSTRACT F THE DISCLOSURE A device for detecting variations in the oxygen content of gases containing small amounts of oxygen, comprising a galvanic 'cell which is provided with a gas compartment wherein a cathode partly extending above electrolyte is exposed to the gas, wherein the size or aggregate size of one or more gas inlet -openings of said compartment is substantially smaller than the size or aggregate size of one or more outlet openings of such compartment, and the size of such compartment and the location of the inlet and outlet openings relative to each other yand to the cathode are such that in use only a portion of the total quantity of gas entering the compartment will reach the cathode and the rest of the gas will leave the compartment without `contacting the cathode.

The present invention relates to a device for indicating variations in the oxygen content of gases containing small amounts of oxygen.

It is known to detect such variations by passing the gas into a galvanic cell of which the cathode which is resistant to the electrolyte, made of a non-porous metal land is only partly immersed in the electrolyte, and the anode consists of a base metal which is easily attacked by the electrolyte in the presence of oxygen. The gas contained in the oxygen is reduced at the cathode, and the intensity of the electric current thereby produced is a function of the oxygen concentration of the gas.

It is quite practicable to make such a device with a sensitivity such that, at a ow rate of the gas to be examined equalling 50 cm.3 per minute, an oxygen concentration of one part per million is indicated as a current intensity of about 3 microamperes, and a galvanometer may be used which is capable of indicating a change in current intensity as small as 1 microampere. However, the known construction of meter is not suitable for obtaining -a larger response range than corresponds to oxygen concentrations from about 0 to 30 parts of oxygen per million. At higher concentrations the sensitivity decreases, and the meter becomes almost insensitive at an oxygen concentration of 1000 parts per million.

One of the aims of the invention is to provide a meter with a higher measuring range.

A device, according to the invention for detecting variations in the oxygen content of gases containing small amounts of oxygen, comprises a galvanic cell which is provided with a gas compartment wherein a part of the cathode extending above the electrolyte is exposed, and which when connected to ra galvanometer yields a current dependent on the oxygen content of gas passed through such compartment, wherein the size or aggregate size of the gas inlet opening or openings of said compartment is substantially smaller than the size or aggregate size of the gas outlet opening or openings of such compartment, and .the size of such compartment and the location of the inlet and outlet openings relative to each other and to the cathode are such that in use a proportion 3,398,358 Patented Aug. 20, 1968 ice of the total quantity of gas entering the compartment will leave the compartment without contacting the cathode. Prefer-ably the size ratio of the inlet opening(s) to the outlet opening(s) is such that in use, the :pressure of the gas in the gas compartment will substantially correspond with atmospheric pressure.

When a device according to the invention is used, not all of the oxygen contained in the gas is reduced at the cathode, but this is no objection as the sensitivity of the device can be high enough for measuring, e.g. 20% of the -oxygen contained in the gas.

To measure concentrations of oxygen higher than about 30 parts per million with the known meter, the gas t0 be examined had first to be diluted, and the degree of dilution had to be very accurately controlled to permit the real oxygen concentration to be calculated from the meter reading. However, if a meter according to the invention is appropriately designed as regards the size of the gas compartment, the sizes of the inlet and outlet openings for the gas `and the disposition of -these 0penings relative to each -other and to the cathode it is possible to measure oxygen concentrations up to, say, 5000 parts per million with a meter of the same order of size as or even smaller than the known meter.

In view, inter alia of the temperature sensitivity of the meters, it is desirable, to use low flow rates. With the known device, however, these low flow rates have the drawback that they have to be kept constant. Devices according to the invention on the other hand are less sensitive to changes in the flow rate of the gas. If the aforesaid factors of sizes and spatial arrangements are appropriately chosen, flow `rate changes will have only a slight effect at the cathode. Between 4 and 10 liters per hour the sensitivity of the particular meter now to be described ywith reference to FIG. 1 of the accompanying drawings is even completely independent of Ithe gas ow rate.

Brie)c description of the drawings FIGURE 1 is a longitudinal sectional view of an apparatus embodying the invention;

lFIGURE 2 is a graphic view developed from use of the FIGURE 1 apparatus, showing oxygen concentration versus current intensity; and

FIGURE 3 is a graphic view developed from use of the FIGURE 1 apparatus, showing current intensity versus time.

Referring to FIG. 1, the meter comprises a gas compartment or vessel 1 provided with a cooling jacket 2 having supply and discharge branch pipes 3 and 4 to keep the vessel at a constant temperature. A holder 5 for an anode 6 and a conductor 7 reaches into the vessel 1. The holder is provided with large openings 8. Furthermore, it is fitted with a stopper 9 containing a holder 10 for a cathode 11. The holder 10 also serves as inlet for the gas to be examined, which is supplied through a branch pipe 12 and a cock 13, and issues through four small apertures 14 to enter the space over the electrolyte 15.

The gas leaves the space via the stopper 9, the cock 13, and a branch pipe 16, 17 indicates a conductor which is connected to the cathode 11. The said cathode may, for instance, be made of silver gauze having meshes per cm?.

The gas entering the cell through the small apertures 14, leaves it as a virtually free flow, since the exit has a much larger passage area throughout. Only part of the gas, and, hence, also only part of the oxygen, reaches the cathode 11. A change in the rate of ow of the gas in the holder 10 has little or no effect on the results of the measurement, as the amount of gas passing the cathode remains relatively constant. For the only result of a change in the rate of tlow of the gas inlet 10 is that the quantity of gas that is immediately discharged and does not reach the cathode is charged the same way. AOnly of the oxygen supplied is bound at the cathode. Owing to the diffusion of the infed gas into the gas present in the cell, the relation between the concentration and the measured current intensity is substantially linear up to a concentration of about 250 parts of oxygen per million (p.p.m.). This is a very important advantage of the device and is made apparent by FIG. 2 of the 4accompanying drawings in Which the oxygen concentration is plotted against the measured current intensity. FIGURE 3 of the accompanying drawings shows that at Various oxygen concentrations the device responds almost immediately and that within 3 minutes the current intensity is at about 90% of its ultimate value which means that, in spite of the use made of a dilusion cell, the device is not inferior in regard to response time, to the known device 'hereinbefore referred to.

We claim:

1. A -galvanic cell of the type used in detection of variations in oxygen content of gases containing small amounts of oxygen, said galvanic cell having means dening a gas compartment therein; an electrolyte partly lling said compartment; a cathode partly submerged in said electrolyte and extending thereabove for exposure to gas within said compartment; means defining at least one gas inlet opening into said compartment above the electrolyte; means defining a gas outlet from said compartment above the electrolyte, the aggregate size of said at least one gas inlet means being substantially smaller than the aggregate size of said gas outlet means and said ygas outlet means being located so near said at least one gas inlet means that -a portion of the gas entering said compartment through said at least one gas inlet means, leaves said compartment 4 through said gas outlet means before having contacted said cathode, whereby lonly a remainder portion of the gas entering said compartment through said at least one gas inlet means contacts said`cathode.

2. A galvanic cell of the type used in detection of variations in oxygen content of gases containing small amounts of oxygen, said galvanic cell having a gas compartment partly lled with electrolyte and having at least one gas inlet thereto and at least one gas outlet therefrom; a cathode in 'the gas compartment; part of the cathode within the gas compartment being exposed above the electrolyte; the aggregate size of the gas inlet of said compartment being substantially smaller than the aggregrate size of the gas outlet of such compartment, andthe size of such compartment and the location of the gas inlet and outlet relative to each other and to the cathode being such that, in use, a proportion of the total `quantity of gas entering the compartment will leave the compartment without contacting the cathode.

References Cited UNITED STATES PATENTS 1,472,125 10/ 1923 Keeler 324-30 2,992,170 7/ 1961 Robinson 324-29 3,028,317 5/1962 Wilson et al. 324-29 3,049,664 8/ 1962 `lacobson et al 324-29 3,234,117 2/1966 Rost et al 204-195 3,258,411 6/ 1966 Hersch 204--1 3,269,924 9/ 1966 Nessler 324-30 RUDOL'PH V. ROLINEC, Primary Examiner.

C. F. ROBERTS, Assistant Examiner. 

